Method of obtaining exceptional formability in aluminum bronze alloys

ABSTRACT

The instant disclosure teaches a method of obtaining exceptional formability in aluminum bronze alloys comprising: providing an aluminum bronze alloy containing from 8.0 to 11.8 percent aluminum plus 0.5 to 5.0 percent iron, balance essentially copper, cold working said alloy and annealing from 1,000* to 1,400* F. and superplastically deforming at 1,400* to 1,600* F.

United States Patent Eichelman, Jr.

[451 Apr. 4, 1972 References Cited 3,287,180 11/1966 Eichelman, Jr. etal ..148/1 1.5 R 3,290,182 12/1966 Eichelman, Jr. et a1 ..148/1 1.5 R 3,347,717 10/1967 Eichelman, Jr. et a1 ..148/1 1.5 R 3,399,084 8/1968 Eichelman, Jr. et a] ..148/11.5 R 3,464,865 9/1969 Eichelman, Jr. ..148/1 1.5 R

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-W. W. Stallard Att0rney-Gordon G. Menzies and Robert H. Bachman [57] ABSTRACT The instant disclosure teaches a method of obtaining exceptional formability in aluminum bronze alloys comprising: providing an aluminum bronze alloy containing from 8.0 to 1 1.8 percent aluminum plus 0.5 to 5.0 percent iron, balance essentially copper, cold working said alloy and annealing from l,000 to 1,400 F. and superplastically deforming at l,400 to UNITED STATES PATENTS 1,600 F 3,l76,410 4/1965 Klement ..75/162 17 Claims, 1 Drawing Figure L/M/T 0F moss/m0 TRAVEL f5 ..62 400 i m 4.1

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TEMPERATURE E [[G- 2 INVENTORZ GEORGE h. E/CHELMAN. JR.

BY V 01:2, 3M

AGENT Patented April 4, 1972 3,653,980

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Z NO/lV9NO73 INVENTOR' GEORGE h. E/CHL MAN. JR.

AGENT METHOD OF OBTAINING EXCEPTIONAL FORMABILITY IN ALUMINUM BRONZE ALLOYS The present invention relates to a method for obtaining exceptionally high formability of aluminum bronzes, and the article produced thereby.

Typically, the aluminum bronze alloys are well-known for good formability at elevated temperatures, i.e., they may be readily hot rolled, forged, or extruded when in the all beta or predominantly all beta phase condition at elevated temperatures. Such alloys are extremely versatile and have a wide variety of uses. exemplicative of which are: corrosion resistance parts, such as condenser tubes or valves; metal bellows and springs where strength and fatigue resistance are important; heat resistance parts in which the resistance to corrosion at high temperatures is required, such as parts for internal combustion engines; wear resistance parts such as guides and ways, and metal and glass forming dies.

The method of the present invention provides for super plasticity of the iron containing aluminum bronze alloys at elevated temperatures. Aluminum bronze alloys exhibiting superplasticity would particularly find wide application in vacuum forming processes wherein high tensile properties are desired in the formed part. In addition, the process of the present invention is also readily applicable to the manufacture of articles of intricate shapes by forcing the aforementioned alloys into molds or dies while in the super plastic state and thereby taking advantage of the increased plasticity of the alloys.

Accordingly, it is a principle object of the present invention to provide a process as aforesaid which is characterized by plasticity heretofore unattained in alloys of this type at elevated temperatures.

It is a further object of the present invention to provide a process as aforesaid which attains this greatly improved physical property without degredation of other properties so desirable in alloys of this type, and the article produced thereby.

It is still a further object of the present invention to provide a process as aforesaid conveniently, expeditiously and at reasonable costs.

Further objects and advantages of the present invention will appear hereinafter.

In accordance with the present invention it has now been found that the foregoing objects and advantages may be radily accomplished.

The process of the present invention comprises; (A) providing an aluminum bronze alloy comprising from 8.0 to 11.8 percent aluminum and from 0.5 to 5.0 percent iron, balance essentially copper, (B) cold reducing said alloy and annealing said alloy at a temperature from about l,000 to l,400 F. for at least 2 minutes (C) superplastically deforming said alloy in the temperature range of about l,300 to l,700 F. and preferably in the range of l,400 to l,600 F.

If high tensile properties are particularly desired, after the deforming of step (C) into the desired shape the formed article may be rapidly cooled to at least below 1,000 F. in order to retain a high proportion of beta phase and to convert the beta phase to martensite as, for example, with a water or oil quench while the formed article is in the mold, or by forming into cold molds.

The purpose of the aforementioned step (B) is to insure optimum refinement of the grain structure of the alloy. The maximum time of annealing is not critical so long as grain growth does not become excessive, but is generally not longer than about 2 hours. Step (B) is preferably repeated at least once, and is preferably repeated a plurality of times, in order to insure obtaining a requisite fine grain size. The grain size is normally less than about 0.065 mm and generally ranges from about 0.005 to 0.020 mm.

The percentage cold reduction of step (B) although not critical is preferably at least percent, and more preferably is at least 50 percent, and generally ranges from about 40 to about 90 percent.

Naturally, the alloy after the aforementioned cold reducing step need not be annealed since the alloy will recrystallize to the requisite fine grain structure at the deforming temperature.

As an alternative embodiment of the present invention the alloy provided may be hot reduced at a temperature of from about l,000 to 1,400 rather than cold reducing as in step (B) in order to refine the grain structure of the alloy, thus eliminating the need of annealing. The alloy is preferably hot reduced at least 20 percent and preferably for a plurality of times while in the aforementioned temperature range in order to develop the requisite fine grain structure. The alloy may then be deformed as in step (C) The aforementioned alloying substituent of iron contributes to the development of the requisite fine grain size.

Naturally impurities may also be present such as, for example, tin, zinc, lead, nickel, silicon, silver, phosphorus, magnesium, antimony, bismuth, and arsenic.

The surprising super plasticity found when the aforementioned alloys are processed in accordance with the present invention appears to be associated with thecombination of the relatively small grain size of the alloy and the proportions of the alpha and beta phases in the alloy at the forming temperature of about 1,300 to l,700 F.

At the forming temperature of step (C) the proportion of the beta phase in the alloy may range from nil up to substantially percent, depending upon the aluminum content in the alloy and the temperature, i.e., the aluminum content within the range of 8.0 to l 1.8 percent. Optimumly, however, the beta phase content ranges from about 40.0 to 70.0 percent which corresponds to an aluminum content of about 9.0 to 10.0 percent over the given temperature range.

The optimum beta content of about 40.0 to 70.0 percent allows a higher strain rate to be employed for a given elongation in the forming of step (C) and is thus of practical importance as, for example, in providing for increased production of formed articles.

Superplasticity is felt to result in this instance from grain boundary sliding thereby allowing the grains to easily move past each other, without the occurance of grain coarsing. With the presence of the beta structure in the alloy, optimumly from about 40.0 to 70.0 percent, even greater plasticity results which is apparently due to the ease with which it can accommodate deformation of the less plastic alpha grains.

In accordance with the present invention, the deformation or forming is such as to provide for superplasticity and normally conforms to a strain rate of less than about 3.0 per minute and preferably about 0.5 perminute or less for applications where a particularly high elongation is desired. Normally, the strain rate of the present invention ranges from about 0.03 per minute to about 0.5 per minute for practical considerations.

The strain rate of the present invention is defined as the cross head speed in inches per minute divided by the initial gage length of 2 inches, conforming to the test conditions employed with tensile specimens, which equals a numerical value.

Following the deformation of step (C) and the aforementioned rapid cool following step (C) the formed article may be tempered if desired, at a temperature range of from about 500 to 900 F. for at least 5 minutes and preferably from 600 to 750 F. and preferably not longer than 4 hours in order to avoid coarsing of the structure, in order to develop a higher tensile strength and a particularly higher yield strength.

Naturally, if a slow cool, such as a normal air cool, is employed the formed article may be reheated to the temperature range of l,l00 to l,800 F., and then rapidly cooled and tempered.

It is to be noted, however, that relatively high tensile and yield strengths are attained wherein a normal or slow cool is employed, without further treatment, i.e., a yield strength of about 40,000 psi and a tensile strength of about 100,000 psi.

Thus, the present invention is applicable to an aluminum bronze having a fine grain size and containing the beta phase with preferred beta phase content ranging from about 40.0 to 70.0 percent, and provides formed articles characterized by high tensile properties.

The present invention will be more readily apparent from a consideration of the following illustrative examples:

EXAMPLE I An aluminum bronze alloy containing 9.8 percent aluminum, 4 percent iron the balance essentially copper was chill cast in the form of l X l X 4 V2 inch bar and processed to 0.050 inch gage by hot rolling and cold rolling and annealing at l,l50 F. a plurality of times resulting in a grain size of 0.010 mm in diameter. The alloy was then pulled in tension at a cross head speed of 1.0 inch per minute (05 min. after reheating to l,450 F. The samples tested were of 0.050 inch strip with a gage length of 2.0 inch and a gage width of one half inch and tested at a cross head speed of l inch per minute. The elongation was found to be uniform and about 400 percent. This elongation was essentially free of local necking in the fracture characteristics of super plasticity.

EXAMPLE II The alloy of Example I was subsequently water quenched after a forming operation and then tempered at 650 F. for 1 hour.

Tensile testing showed an ultimate tensile strength of the alloy of about 150,000 psi and a yield strength of 1 10,000 psi.

EXAMPLE lll FIG. I shows the elongation properties of a series of copperaluminum alloys containing about 4.0 percent iron when tested at various temperatures and having varying beta contains at a cross head speed of 1 inch per minute (0.5 min. It is seen that the percent elongation increases as the proportion of the beta phase changes to within the range of about 40.0 to 70.0 percent.

EXAMPLE lV FIG. 11 shows the elongation properties of a copper aluminum alloy containing 9.8 percent aluminum and 4.0 percent iron, balance essentially copper at a cross head speed of 1.0 inch per minute and 6 inch per minute (0.5 min. and 3.0 min. at varying temperatures. This figure clearly shows the increase of plasticity of the alloy as the strain rate decreases. It is to be noted that due to limited cross head travel 370 percent elongation is the upper value of testing, and thus higher elongation values for the 9.8 percent aluminum, 4 percent iron alloy at a cross head speed of l inch/min. is anticipated. The reported higher value resulted from elongation of the sample during removal from the furnace.

EXAMPLE V FIG. 111 shows the elongation properties of the alloy of Example lll versus beta content of the alloy when pulled in tension at a cross head speed of 0.1 and 1 inch per minute (0.05 min. and 0.5 min.

This example clearly shows the general rise in plasticity of the alloy as the beta content increases. generally.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. A method of obtaining exceptional formability in aluminum bronze alloys, which comprises:

A. providing an aluminum bronze alloy consisting essentially of 8.0 to l 1.8 percent aluminum and from 0.5 to 5.0 percent iron, balance copper.

B. cold reducing said alloy.

C. annealing said alloy at a temperature from l,000 to 1,400 F. for at least 2 minutes,

D. superplastically deforming said alloy in the temperature range of 1,300 to l,700 F.

2. The method of claim 1 wherein said deforming is at a strain rate of less than 3.0 per minute.

3. The method of claim 1 wherein said deforming is at a strain rate of 0.03 to 0.5 per minute.

4. The method of claim 2 wherein steps B and C are repeated at least once and said reducing is at least 10 percent.

5. The method of claim 2 wherein said alloy contains from 9.0 to 10.0 percent aluminum.

6. The method of claim 4 wherein said strain rate is from 0.03 to 0.5 per minute.

7. The method of claim 6 wherein said beta content is from 40.0 to 70.0 percent.

8. The method of claim 6 wherein the temperature of deforming is from 1,400 to l ,600 F.

9. The method of claim 7 wherein said annealing is from 2 minutes to 2 hours.

10. The method of claim 9 wherein following step (D) said alloy is rapidly cooled and then reheated to the temperature range of from 500 to 900 F. for at least 5 minutes.

11. The method of claim 10 wherein said reheating is not longer than 4 hours.

12. A method for obtaining exceptional formability in aluminum bronze alloys. which comprises:

A. providing an aluminum bronze alloy consisting essentially of 8.0 to l 1.8 percent aluminum and from 0.5 to 5.0 percent iron, balance copper,

B. hot working said alloy in the temperature range of from 1,000" to 1,400 F,

C. superplastically deforming said alloy in the temperature range of 1,300 to l,700 F.

13. The method of claim 12 wherein said deforming is at a strain rate of less than 3.0 per minute.

14. The method of claim 12 wherein said deforming is at a strain rate of 0.03 to 0.5 per minute.

15. The method of claim 13 wherein the temperature of deforming is from 1,400 to 1,600 F, and said hot working is at least 20%.

16. The article produced by the method of claim 1.

17. The article produced by the method of claim 10. 

2. The method of claim 1 wherein said deforming is at a strain rate of less than 3.0 per minute.
 3. The method of claim 1 wherein said deforming is at a strain rate of 0.03 to 0.5 per minute.
 4. The method of claim 2 wherein steps B and C are repeated at least once and said reducing is at least 10 percent.
 5. The method of claim 2 wherein said alloy contains from 9.0 to 10.0 percent aluminum.
 6. The method of claim 4 wherein said strain rate is from 0.03 to 0.5 per minute.
 7. The method of claim 6 wherein said beta content is from 40.0 to 70.0 percent.
 8. The method of claim 6 wherein the temperature of deforming is from 1,400* to 1,600* F.
 9. The method of claim 7 wherein said annealing is from 2 minutes to 2 hours.
 10. The method of claim 9 wherein following step (D) said alloy is rapidly cooled and then reheated to the temperature range of from 500* to 900* F. for at least 5 minutes.
 11. The method of claim 10 wherein said reheating is not longer than 4 hours.
 12. A method for obtaining exceptional formability in aluminum bronze alloys, which comprises: A. providing an aluminum bronze alloy consisting essentially of 8.0 to 11.8 percent aluminum and from 0.5 to 5.0 percent iron, balance copper, B. hot working said alloy in the temperature range of from 1, 000* to 1,400* F, C. superplastically deforming said alloy in the temperature range of 1,300* to 1,700* F.
 13. The method of claim 12 wherein said deforming is at a strain rate of less than 3.0 per minute.
 14. The method of claim 12 wherein said deforming is at a strain rate of 0.03 to 0.5 per minute.
 15. The method of claim 13 wherein the temperature of deforming is from 1,400* to 1,600* F, and said hot working is at least 20%.
 16. The article produced by the method of claim
 1. 17. The article produced by the method of claim
 10. 